The formation of struvite (ammonium magnesium phosphate; MgNH.sub.4 PO.sub.4) urinary calculus, which occurs most frequently among urinary calculuses or urolithes of dogs and cats, is mainly caused by an increase in urine pH.
The struvite urinary calculosis or urolithiasis in cats occupies about 88% of urinary calculosis, and said calculus is composed of struvite as ammonium magnesium phosphate hexahydrate, a small amount of calcium apatite, ammonium urate and uric acid. The struvite urinary calculosis (urolithiasis) is principally caused by saturation of the concentration of ammonium magnesium phosphate in urine, depending on species of a diet to be fed, a shortage of water supply, a lack of exercise or others, and is further attracted by a urinary infection of a urease-producing microorganism.
With regard to methods for nutritionally preventing urinary calculus, there have been reported (1) a technique increasing the amount of urination by means of raising the water intake, (2) a technique wherein a diet to be supplied is modified or changed gradually from a wet food to a dry food (a solid dry food), (3) a technique which comprises restricting the intakes of magnesium components and phosphorus components in a diet and increasing the contents of sodium salts in the diet, (4) a technique where a urine-acidifying agent is administered for acidification of urine, and others.
The technique using the urine-acidifying agent makes a profit from the fact that the urine pH of 6.6 or more frequently causes the struvite urinary calculus and, conversely, the urine pH of 6.5 or less reduces the formation of the calculus.
The administration of the urine-acidifying agent is, among these techniques, effective for maintaining the urine acidic so as to dissolve the struvite urinary calculus as well as for preventing the formation of the urinary calculus.
As the urine-acidifying agent, there have been reported, for example, DL-methionine, ammonium chloride, ascorbic acid (vitamin C), ethylenediamine dihydrochloride, sodium hydrogenphosphate and the like.
The use of these urine-acidifying agents, however, has disadvantages that it may cause a disorder depending on the dose of the urine-acidifying agents. For example, it has been reported that an excessive intake of methionine is harmful and that administration of a urine-acidifying agent, especially DL-methionine, ammonium chloride, is not recommended since it has a plural of disadvantages such as a poor palatability, thus causing dysorexia or vomition, enhancing intoxication or growth retardation [Clinical Nutrition in Small Animals III, Lon D. Lewis et al., published by Mark Morris Research Center, Oct. 31, 1989, pp. 9-41 to pp. 9-46, and R. Wolter's Nutrition in Cats and Dogs, R. Wolter, published by Nihon Rinsho-sha, Mar. 20, 1991, pp. 223-232.].
The struvite urinary calculosis among whole urinary calculosis in dogs occurs in a proportion of about 80 to 97% in female and immature male dogs, and about 50 to 75% in matured dogs, hence the occurrence thereof takes overwhelmingly major as compared with other urinary calculosis such as urinary calculus caused by calcium oxalate, ammonium urate, cystine, or a salt of silicic acid. It has been known that the urinary calculosis may also be caused by suppression of urination, a shortage of exercise, obesity, gonadectomy and other factors. Further, the formation of the struvite urinary calculus is liable to be promoted by supplying a dog with a food containing a high concentration of magnesium, salts of phosphoric acid and calcium components, and such formation is also induced by infection of a urease-producing microorganism.
There has been known as techniques for preventing or treating the urinary calculosis in dogs that (5) a technique wherein a urinary infectious disease is radically cured or controlled with the use of a suitable antibiotic; (6) a technique which comprises increasing the intake of sodium chloride or saline for promoting urination; (7) a technique where a diet for dissolving calculus is supplied; (8) a technique which comprises administering a urease-inhibitor such as acetohydroxamic acid to a dog of urinary infectious disease caused by a urease-producing microorganism; (9) a technique which comprises administering the urine-acidifying agent, and others.
The administration of acetohydroxamic acid in a dose of 25 to 100 mg/kg of body weight per day is effective on suppressing the urease activity in urine, lowering the urine pH, reducing crystalline urine, and, still more, dissolving the urinary calculus. Said administration, however, may bring about hemolytic anemia, and in a certain species of dog, show a teratogenicity. Further, it has been reported that the use of the urine-acidifying agent is not also recommended similarly as mentioned above in cats [Clinical Nutrition in Small Animals III, Lon D. Lewis et al., published by Mark Morris Research Center, Oct. 31, 1989, pp. 10-3 to pp. 10-40, and R. Wolter's Nutrition in Cats and Dogs, R. Wolter, published by Nihon Rinsho-sha, Mar. 20, 1991, pp. 237-245].